It is common practice at the present time to provide a door, particularly a door which is provided as an "outside.revreaction. door for a dwelling or other space, with a knob set which may or may not have a lock therein and also with a separate lock of the "deadbolt.revreaction. type. The term "outside.revreaction. as thus used is intended to mean the primary access to a space and can include the main entrance to an apartment or office within a larger structure. With solid wooden doors, the door is commonly manufactured with no lock openings and the carpenter or locksmith who installs the door simply cuts the necessary openings.
However, in the case of hollow doors, particularly hollow metal doors, it is more difficult to accurately and neatly locate and cut the necessary openings to receive a knobset, lockset or lock at the point of installation using conventional hand tools. For this reason, it is desirable to provide such openings at the time of manufacture. It is particularly important to provide a rectangular opening in the door edge to receive a plate having an opening through which the lock bolt is to pass since that opening is the most difficult to locate and cut at the installation site.
However, the manufacturer usually does not know what kind of lock will ultimately be installed in the door. It is well known that deadbolt locks produced by different lock manufacturers have various physical configurations. For example, it is possible that a deadbolt lock may be installed independent of a "standard.revreaction. lockset of the type including a knobset with a lock incorporated therein. It is also possible to install a combination unit including the knob assembly with a lock incorporated therein and a separately lockable deadbolt lock as part of the same assembly. Because of the fact that combination units made by various manufacturers are not standardized completely, the vertical spacing between the knob centerline and the deadbolt centerline can vary. The door manufacturer is therefore faced with the problem of not knowing what kind of plate to provide to fit the rectangular opening and to have a bolt hole which will be at a proper vertical distance from the knob centerline so as to permit passage of the bolt of the lock to be ultimately installed. Even in the case of independently mounted lock and knob devices, it is often desirable to have some flexibility in mounting location. Furthermore, the metal cover plates furnished with the deadbolt locks are provided in different widths and it is desirable to provide some technique for adapting to this variation.
It has previously been proposed to provide a cover plate which is adjustably attachable in the opening. However, this has serious disadvantages. For one, the plate is difficult to position in the rectangular opening with sufficient accuracy such that the deadbolt can reliably and smoothly pass through the opening therein. Additionally, if the adjustability is provided by using elongated openings for the fasteners holding the plate to the door, it is possible for the fasteners to loosen slightly in time, thereby permitting the plate to slip and bind against the bolt, rendering the lock difficult to operate or completely useless.
A further difficulty arises from the fact that the horizontal spacing between the knob centerline and the door edge, referred to as "backset,.revreaction. is nonstandard in the sense that it can be any one of at least two dimensions.